Restyle to a clean, flat look and rename brand to SCOPENET

- Brand is now SCOPENET everywhere (defaults, UI, installer, docs)
- Launcher: solid backgrounds (no animated orbs/grain), flat Play button
  without gradient/shine/glow, quieter rail with a simple active
  indicator, smaller type scale, Inter as default font, glass off by
  default, restyled sliders
- Panel: same flat treatment; live preview mirrors the new launcher
- New flat scope-reticle logo and app icons
- Calmer default palette
- Fix: lock the shared cargo cache in the Docker build (amd64/arm64 raced)
- Fix: Windows-only clippy lint in sys.rs

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

panel/web/src/App.svelte

@@ -13,7 +13,7 @@
   import { logout, session, type Me } from './lib/session.svelte';
   import { toast } from './lib/toast.svelte';
 
-  let brand = $state<{ name: string; logo_url: string | null }>({ name: 'ScopeNet', logo_url: null });
+  let brand = $state<{ name: string; logo_url: string | null }>({ name: 'SCOPENET', logo_url: null });
   let checking = $state(!!session.token);
 
   $effect(() => {
@@ -75,6 +75,6 @@
   .shell { display: flex; min-height: 100vh; }
   main { flex: 1; min-width: 0; }
   .boot { height: 100vh; display: grid; place-items: center; }
-  .pulse { width: 42px; height: 42px; border-radius: 12px; background: linear-gradient(135deg, var(--accent), var(--accent-2)); animation: pulse 1s ease-in-out infinite alternate; }
+  .pulse { width: 28px; height: 28px; border-radius: 50%; border: 3px solid var(--surface-3); border-top-color: var(--accent); animation: spin 0.8s linear infinite; }
   @keyframes pulse { from { transform: scale(0.85); opacity: 0.6; } to { transform: scale(1); opacity: 1; } }
 </style>